This study will demonstrate the effects of long-term ingestion of high fat diets on serum prolactin and on induced and spontaneous mammary tumors in rats. The relationship between fatty acid composition of fats and their endocrine and fat diet enhances rat mammary tumorigenesis will be assessed, employing DMBA-induced tumors incidence in rats fed one of several dietary fats. Natural dietary fats of widely varying fatty acid composition will be fed in a purified diet; serum prolactin will be monitored by RIA, and DMBA-induced and spontaneous mammary neoplasms will be identified. The possibility of predicting ultimate tumor response of animals from serum prolactin profiles will be determined by comparison of periodic serum prolactin values at estrus or diestrusy with tumor development. The distribution of prolactin receptors in various mammary lesions will be determined by autoradiographic procedures. Dietary fat effects on the pathogenesis and incidence of spontaneous or induced benign or malignant mammary tumors will be evaluated separately rather than considering effects on all mammary tumors together. This application requests supplementary funds to purchase a gamma counter for use in the prolactin assays.